1. Field of the Invention
This disclosure relates to polymer resins and, in particular, to polymer resins suitable for use in polymer interlayers, including those utilized in multiple layer panels.
2. Description of Related Art
Poly(vinyl butyral) (PVB) is often used in the manufacture of polymer sheets that can be used as interlayers in multiple layer panels, including, for example, light-transmitting laminates such as safety glass or polymeric laminates. PVB is also used in photovoltaic solar panels to encapsulate the panels which are used to generate and supply electricity for commercial and residential applications.
Safety glass generally refers to a transparent laminate that includes at least one polymer sheet, or interlayer, disposed between two sheets of glass. Safety glass is often used as a transparent barrier in architectural and automotive applications, and one of its primary functions is to absorb energy resulting from impact or a blow without allowing penetration of the object through the glass and to keep the glass bonded even when the applied force is sufficient to break the glass. This prevents dispersion of sharp glass shards, which minimizes injury and damage to people or objects within an enclosed area. Safety glass may also provide other benefits, such as a reduction in ultraviolet (UV) and/or infrared (IR) radiation, and it may also enhance the aesthetic appearance of window openings through addition of color, texture, and the like. Additionally, safety glass with desirable acoustic properties has also been produced, which results in quieter internal spaces.
Often, polymers that exhibit one set of desirable properties, such as acoustic performance, lack other desirable properties, such as impact resistance or strength. Therefore, in order to achieve desirable combinations of properties, multilayered polymer interlayers have been used. These multilayered interlayers may include at least one inner “core” layer sandwiched between two outer “skin” layers. Often, the core layer of an interlayer may be a softer layer having a lower glass transition temperature, which enhances its acoustic performance. However, because such resin layers can be difficult to easily process and/or transport, the skin layers of such multilayered interlayers are often stiffer, with higher glass transition temperatures, which imparts enhanced processability, strength, and impact resistance to the interlayer.
However, use of various layers having different properties can also produce optical defects within the interlayer. For example, one defect common to these types of multilayer interlayers is mottle. Mottle is an objectionable form of optical distortion or visual defect appearing as uneven spots or texture, usually in the final structure. Mottle is caused by small-scale surface variations at the interfaces between the soft and stiff layers wherein the individual layers have different refractive indices. Clarity is another important optical property that is determined by measuring the level of haze within the interlayer or panel. High haze typically occurs when different types of optically incompatible polymers and/or plasticizers are blended or mixed together. In such mixtures, light passing through the blend is scattered as it encounters regions of different polymer materials, and the result is a hazy, visually unclear appearance. High clarity polymers and interlayers are those having very low haze values.
Thus, a need exists for polymer resins, resin layers, and interlayers that exhibit desirable optical properties, such as reduced haze and mottle and improved clarity, without sacrificing other properties, including impact resistance and acoustic performance. Such interlayers could be monolithic or multilayered and should be usable in a wide variety of applications, including safety glass and polymer laminates.